Spark plug



V. R. THOMAS Nov. 4, 1952 SPARK PLUG Filed Oct. 22. 1949 lill 1 Patented Nov. 4, 14952 UNITED STATES PATENT rOFFICE.

2 Claims.

able parts by means of a baked cement while leaving the parts free for relative turning and longitudinal adjustment and without detracting from the eiectiveness of the seal.

Other objects and advantages of the invention will become apparent from the following detailed description taken in connection with the accompanying drawings, in which Figure 1 is an elevational view of a spark plug embodying the novel features of the present inventiOn.

Fig. 2 is a section taken along the line 2-2 of Fig. l.

Fig. 3 is a sectional view taken along the line 3 3 of Fig. 2.

While the invention is susceptible of various modications and alternative constructions, I have shown in the drawings and will herein describe in detail the preferred embodiment. It is to be understood, however, that I do not intend to limit the invention by such disclosure but aim to cover all modifications and alternative constructions falling within the spirit and scope of the invention as expressed in the appended claims.

The improved spark plug is similar in general construction to the plugs commonly used in internal combustion engines including a cylindrical metallic shell Il] having an upper portion usually of hexagonal cross section and a lower portion or" reduced diameter externally threaded at II to screw into an opening in the cylinder head of an engine. The center electrode comprises a round rod I2 extending through a tube I3 of hard ceramic material having an internal flange I4 seated against an internal shoulder I5 in the shell I0 and clamped against the latter by a screw plug I6.

The inner gradually tapering end portion Il of the ceramic tube is enclosed by the threaded part of the shell I 0 and by a frusto conical dome i8 integral therewith and having a plurality, four in the present instance, of angularly spaced holes I9 of about .110 of an inch in diameter extending diagonally through the cone. The end of the dome I8 is flat and preferably formed at its center with a hole 20 about .078 of an inch in diameter. The shell IFJ, the dome I8, and the tapered end I1 of the tube cooperate to define an auxiliary combustion chamber 2l around the end 22 of the center electrode I2 which end faces toward and is disposed parallel to the inner at surface 23 of the dome I 8 with which the electrode cooperates to define a spark gap of the desired width. A large sparking area is thus provided so as to insure proper combustion of the gas within the chamber 2 I followed by rapid propagation of the resulting flame outwardly through the holes I9 and 2B in a plurality of jetlike streams. Very eflicient ignition of the main mass of combustible gas in the enginecylinder is thus achieved.

Provision is made for adjusting the center electrode I2 axially by means of a tool engaging the electrode at a point exteriorly of the plug. For this purpose, the outer half portion of the rod I2 is larger than the electrode end and is threaded into an elongated nut 24 cemented tightly into a cylindrical counterbore 25 in the ceramic tube I3. A slot 2S or other tool receiving recess is formed in the outer end of the screw to enable the rod to be turned within the nut and the electrode end 22 to be advanced toward or away from the surface 23 of the grounded electrode. a

The smooth inner end portion of the electrode rod I2 extends loosely through a bore 2 in the ceramic tube and, in accordance with the present invention, a thermally set seal of ordinary spark plug cement is formed between the opposed surfaces of the electrode rod and the ceramic tube preferably extending throughout the length of the bore 2l as indicated at 28 and over part of the axial length of the recess within the counterbore 25 between the inner end thereof and the end of the nut 24 as indicated at 29. The cement employed is ordinary spark plug cement which. after baking at about degrees F. for several hours, becomes a hard mass having about the same heat conductivity as the ceramic of the tube I3.

Provision is made for forming the seals 28 and 29 while preventing adherence of the cement to the surface of the rod l2 so that the latter, after baking of the cement, may be turned within the seals and advanced axially by the action of the screw and nut. This is accomplished by applying to the surface of the rod before application of the cement and extremely thin film of any material of waxy or oily character capable of penetrating into'the pores of the metal of the rod l2 or adhering well to the surface thereof Without being absorbed by the coating of cement so as to prevent direct and intimate contact between the cement and the metal surface during baking of the cement. A relatively light oil known to the trade as detergent oil has been found to be particularly satisfactory.

To form the cement seals 28 and 29 and also a seal 30 around the nut 24, the nut and screw are assembled and the lower projecting end portion of the rod l2 is first dipped inthe oily liquid above referred to. Then a coating of spark plug cement is painted over thev entire outer Asur-- face of the rod and the nut. Next, a similar coating of the cement is applied to the interior surface of the ceramic tube B3. The rod and ynut assembly are then pressed into the tube to bring the parts into their final relationship. Some of the cement is thus forced' out through lthe-bore 2l, but enough cement remains in the oounterbore 25 to form the seal 29 and while adapted to conduct heat nearly as rapidly as the ceramic of Athe tube. As used in the claims, a film of lubricant contemplates that portion of oil present between the engaging surfaces of the rod l2-and the cement after dippingof the rod in the oily liquid and baking of the cement around the rod.

With the seals 28 and 29 thus formed, the rod l2 is relatively free to turn within the hardened cement bodies, and, as a result', the rod may be adjusted axially to vary the width of the spark gap. During the advance of the rod to narrow the gap, the enlarged or threaded portion of the rod moves into the recess 3l which is longer than the maximum adjustment required during the full service life of the spark plug. Moreover, the rod I2 remains free for turning throughout the service life of the plug.

To increase the effectiveness of the seal in preventing the escape of gases outwardly .through the tube, a gasket, 32, preferably comprising a washer of soft metal such asa lead-antimony alloy, nts `snugly around the Vscrew and is compressed tightly against the outer end vof the .ceramic tube-by means of a nut 33,. A cap 34 threaded onto the. outer end of the screw provides a suitable terminal for attachment of. the ungrounded conductor to the plug.

I claim as my invention:

1. A spark plug comprising an elongated rigid tube of insulation having an axial cylindrical bore extending through one end portion, the remaining portion being counterbored, a nut rigid with said tube and projecting into the o-pen end of the counterbore, an elongated metal electrode rod extending axially through said .tube and having one end portion threaded into said -nut to permit of adjustment of the rod axially of the tube, the other end portion of the rod having a smooth external cylindrical surface smaller than said bore and extending from the counterbore through said bore beyond the open end of the latter, a gasket ring surrounding said electrode adjacent the open end of said counterbore, means compressing said gasket ring around said electrode and against said tube to form a seal, a hollow metallic shell surrounding said tube intermediate the ends thereof and rigidly supporting the tube, a second electrode on said shell cooperating with the rod end adjacent said bore to define a spark gap, and means providing a gastight seal around said rod within said bore permitting free turning of the rod and advance of the latter axially comprising a layer of thermally hardened spark plug cement closely surrounding said cylindrical rod surface and filling the annular spa-ce between the rod and the wall of said bore and extending into the inner end portion of said counterbore short of the thread 0n said rod, and a iilm of lubricant between the opposed `surfaces of said rod and said cement layer over the entire engaging areas thereof preventing adherence of said surfaces together.

2. A spark plug comprising an elongated tube of insulation having an axial cylindrical bore extending through one end portion thereof, a nut rigid with the other end portion of said tube, an elongated metal electrode rod extending axially through said tube and having one end portion threaded into said nut to permit of adjustment of the rod axially of the tube, the other end portion of the rod having a smooth external cylindrical surface smaller than and projecting through said bore, a gasket ring surrounding said electrode adjacent said nut, means compressing said gasket -ri-ng around said electrode and against said other end portion of said tube to form a seal, a hollow metallic shell surrounding said tube intermediate the ends thereof and rigidly supporting the tube, a second relectrode on said shell cooperating lwithsaid projecting end of said rod to define a spark gap, and means providing a gas-tight seal around said rod within said bore permitting free turning of the rod and advance of the latter axially comprising a layer of thermally hardened spark plug cement closely surrounding said cylindrical rod surface and lling the annular space between the rod and the wall of said bore, and a film of lubricant between the opposed surfaces of said rod and' said cement layer over the entire engagingareas thereof' preventing adherence of thel surfaces together;

VVERNON R. THOMAS.

REFEREISICIESy CITED The following references are of record in the le of this patent:

UNITED STAIES YFATE.NTS

Number Name yDate 1,190,938 Mosler July 11, 1916 1,243,205 Norman Oct. 16, 1917 1,401,585 Collins Dec. 27, 1921 1,710,056 Griiiin Apr. 23, 1929 FOREIGN PATENTS Number Country Date 220,207 Great4 Britain Aug. 14, 1924 

